1. Field of the Invention
The present invention relates to valves of the type having a rotatable valve closure member within a valve body, and, more particularly, relates to improved techniques for adjusting the axial position of the valve closure member and an elastomeric seat carried thereon for reliable sealing engagement with the valve body.
2. Description of the Background
Various types of valves include rotatable closure members which can be manipulated to control the flow of fluid through the valve body. Many of these valves, such as butterfly valves, employ a resilient elastomeric annular seat carried on the rotatable closure member for reliable sealing engagement with the metallic valve body. It is also well known that machining costs can be reduced by providing techniques which enable the closure member, and thus the elastomeric seal, to be adjusted along the axis of the rotatable closure member, so that the closure member can be "centered" within the valve body.
Such prior art valve closure member/valve body centering devices do not, however, satisfy many of the concerns by customers of such valves. Although the techniques of the prior art may achieve the initial axial centering of the valve closure member with respect to the valve body, the prior art generally does not maintain the closure member centered if the valve is subjected to a high shock load, e.g., if the valve is dropped or jarred during shipment or installation. Also, such prior art centering devices are complicated subassemblies which require precision tolerances to maintain the proper centered relationship between the closure member and the valve body. This problem of maintaining the proper centered closure member/valve body relationship is further increased when the valve closure member is a disk, which provides only a small portion of the elastomeric seal in engagement with the valve body when the valve is in the open position.
Accordingly, many valves are manufactured and sold without such centering devices, or are installed in the field with the centering devices not achieving their intended function of properly maintaining the desired axial position between the closure member and the valve body. Accordingly, the elastomeric seal does not continue to sealingly engage the valve body, or is damaged by the forced rotation of the misaligned closure member with respect to the valve body. In either case, valve leakage results in an expensive repair and/or rebuilding operation.
U.S. Pat. No. 2,924,424 discloses a butterfly valve with the disk-shaped closure member which is axially movable with respect to the valve body during use of the valve. A nut threaded to the valve body may be used to fix the axial position in one direction of a disk with respect to the valve body, with the disk travel in the axially opposite direction toward the valve actuator being resisted by a spring.
The butterfly valve disclosed in U.S. Pat. No. 4,006,883 includes a fitting member threadably connected to the valve closure member at one end, with the opposite end of the fitting member projecting through a threaded aperture in a plate secured to the valve body. A shaft may thus be rotated for adjusting the axial position of the disk within the valve body.
A centering device shown in U.S. Pat. No. 4,036,468 includes a nut axially fixed with respect to valve body, with a threaded screw connected to the valve closure member and passing through the nut. A slide in the end of the screw allows for rotation of the screw with respect to the nut, and thus axial positioning of the closure member within the valve body.
U.S. Pat. No. 4,273,308 discloses a valve with a centering technique similar to that of the '468 patent. The nut is axially stationary with respect to the valve body, but rotates to axially move the threaded stem passing therethrough, which is connected to the closure member. The axial position of the closure member can thus be adjusted by rotating the nut.
While the prior art thus teaches various techniques for adjusting the axial position of a closure member with respect to the valve body, the art does not disclose a cost effective technique for accomplishing this purpose while simultaneously providing a mechanism which maintains the desired axial position of the closure member with respect to the valve body when the valve is subjected to a high shock load. Moreover, the prior art does not disclose reliable techniques for initially maintaining the desired axial position of the closure member with respect to the valve body during shipment and installation of the valve, and which enable the operator, if necessary, to easily adjust and then maintain this desired axial closure member/valve body position.
The disadvantages of the prior art are overcome by the present invention, and improved techniques are hereinafter disclosed for easily and reliably maintaining the desired axial position of a closure member within a valve body.